1. Field of the Invention
The present invention relates to a stencil printer for printing an image on a sheet or recording medium by wrapping a master or perforated stencil around a print drum. More particularly, the present invention relates to a stencil printer of the type including a stretching member configured to exert a stretching force on a master and master stocking means for stocking the master.
2. Description of the Background Art
A stencil for use in a stencil printer has a laminate structure made up of an about 2 xcexcm to 8 xcexcm thick, thermoplastic resin film and a porous support adhered to is each other. The porous support is formed of Japanese paper or synthetic fibers or a combination thereof. A thermal head or similar heating unit selectively perforates, or cuts, the thermoplastic resin film with heat in accordance with image data to thereby make a master. After the master has been wrapped around a print drum, a press roller or similar pressing member presses a sheet against the outer periphery of the print drum with the result that ink, fed to the inner periphery of the print drum, is transferred to the sheet via the porous portion of the print drum and the perforations of the master, thereby printing an image on the sheet.
During printing, the ink is passed through the fibers of, e.g., Japanese paper constituting the porous support of the master. Therefore, if the fibers are locally entangled in the form of clusters or if the fibers extend across the pores of the resin film, then the ink cannot be smoothly passed through the fibers. As a result, fiber marks appear in the solid portions of the resulting image or thin lines become discontinuous or blurted.
To obviate the above defects ascribable to fibers, there has been proposed a stencil including a porous support thinner than conventional one or consisting only of a thermoplastic resin film. However, the apparent mechanical strength of the conventional stencil is implemented by the porous support. In this respect, the stencil with such a thin porous support or consisting only of a thermoplastic resin film is noticeably lowered in mechanical strength because the thermoplastic resin film is thin.
Generally, the stencil is conveyed by a platen roller and master conveying means positioned downstream of the platen roller in the direction of sheet conveyance to clamping means mounted on the print drum while being guided by a guide plate. Because the print drum rotates, the master conveying means and guide plate should not be positioned excessively close to the print drum, so that they do not interfere with the clamping means. Consequently, the master with low mechanical strength slightly waves due to shrinkage ascribable to perforation, the curl of the film and so forth before the master reaches the clamping means. Should the stencil so waving be clamped by the clamping means, it would crease on the print drum due to the wave and would therefore make the resulting prints defective.
In light of the above, Japanese Patent Laid-Open Publication No. 2001-353949, for example, discloses a stencil printer including a stretching member adjoining the outer periphery of a print drum and configured to stretch a master being wrapped around the print drum, see pages 3 through 5 and FIG. 1. The stretching member prevents the master from creasing on the print drum.
Today, a stencil printer of the type automatically performing a sequence of steps of discharging a used master, making a master, feeding the master, printing and so forth is predominant over the other stencil printers, In this type of stencil printer, the printing step is executed after the master discharging, master making and master feeding steps. However, the problem with the conventional stencil printer, which executes the master making step after the master discharging step, is that the next master cannot be made until the end of the master discharging step, extending so-called first print time.
Japanese Patent Laid-Open Publication No. 2002-103565, for example, teaches a stencil printer including master stocking means configured to stock a master and making the next master in parallel with the master discharging step or during printing, thereby reducing the first print time and therefore enhancing efficient operation, see pages 5 through 11 and FIG. 1.
In Laid-Open Publication No. 2001-353949 mentioned above, considering the fact that the stretching member should not be positioned excessively close to the print drum, the stretching member is configured to be movable between a position close to the print drum and a position remote from the same. Also, in Laid-Open Publication No. 2002-103565, a movable master guide, positioned in the upper portion of the master stocking means, is movable between a position where the guide guides the leading edge of a master toward master conveying means downstream of the master stocking means and a position where the guide does not obstruct the entry of the master in the master stocking means.
A stencil printer can free a master from creases and enhance efficient operation at the same time if provided with both of the stretching member and master stocking member. This configuration, however, increases the cost of the stencil printer because particular moving means must be assigned to each of the stretching member and movable master guide.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication No. 6-293176 and 7-125399.
It is an object of the present invention to provide a stencil printer capable of freeing a master from creases and enhancing efficient operation at the same time without increasing the cost.
A stencil printer of the present invention includes a print drum for wrapping a master therearound, a master making and conveying section for perforating a stencil paid out from a stencil roll while conveying it to thereby produce the master, a master stocking section for stocking the master being conveyed by the master making and conveying section, and a roller pair for conveying the master out of the master stocking section. A movable master guide selectively guides the stencil paid out from the stencil roll to the master stocking section or the roller pair. A stretching member adjoins the print drum and is movable between a contact position where it contacts the stencil present on the print drum to thereby exert a stretching force on the master and a released position where the former is released from the latter. The stretching member and movable master guide are interlocked to each other.
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which:
FIG. 1 is a front view showing a stencil printer embodying the present invention in a stand-by condition;
FIG. 2 is a front view showing the illustrative embodiment in a master feed stand-by condition;
FIG. 3 is a front view showing the illustrative embodiment in a master making condition;
FIG. 4 is a front view showing the illustrative embodiment in a master wrapping condition;
FIGS. 5A and 5B are views each showing a particular configuration of a stretching member included in the illustrative embodiment;
FIG. 6 is a front view showing an alternative embodiment of the stencil printer in accordance with the present invention in a stand-by condition; and
FIG. 7 is a front view showing another alternative embodiment of the stencil printer in accordance with the present invention in a stand-by condition.